* add self compaction method with proper caching (pass in tools, don't refresh sys prompt beforehand) + sliding fallback
* updated prompts for self compaction
* add tests for self, self_sliding_window modes and w/o refresh messages before compaction
* add cache logging to summarization
* better handling to prevent agent from continuing convo on self modes
* if mode changes via summarize endpoint, will use default prompt for the new mode
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Co-authored-by: Amy Guan <amy@letta.com>
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